The invention relates generally to systems that permit users to communicate by means of voice in real time and more particularly to such systems in which the users are connected to each other by patcket network.
At present, human beings and computers use different systems for communication. Human beings use telephone networks, while computers use packet switching networks. The telephone networks are optimized to provide switched-circuit real-time voice communication, while the packet switching networks are optimized to provide non-real time data communications.
Of course, each type of network can be used for the other purpose. When a computer is connected to a telephone network via a modem, the telephone network can be used for data communications, and computer software has become available which permits voice communication on the Internet packet switching network. The difficulty with using a telephone network for data communications or a packet switching network for voice communication is that the optimizations present in each kind of network for its main purpose cause problems when the network is used for the other purpose.
For example, data communications are generally bursty, that is, a computer will send some data and then fall silent for a while. If a telephone circuit is being used for data communication, the circuit remains dedicated to the data communications during the periods of silence, resulting in a waste of resources in the telephone system. On the other hand, in order for a voice communication between two people to be acceptable, there can only be a short round-trip delay between the time a person speaks and the time the person hears a response from the other end of the circuit. Moreover, the delay must remain relatively constant throughout the communication. The telephone system is designed for communications with these kinds of stringent real-time requirements, but packet networks are not. Delay in a packet network is a function of the overall load in the network, and consequently, the network may not be able to consistently satisfy the real-time requirements of voice communications.
Even when used simply for voice communications, the telephone network has problems which are a result of its history. The modern telephone network was designed at a time when computer systems were large, expensive, and required specialized operating environments. As a consequence of this, devices xe2x80x9cinsidexe2x80x9d the network, such as switches and network control points, were xe2x80x9cintelligentxe2x80x9d (i.e., they were programmable), while devices at the edges of the network, such as telephones and answering machines, were xe2x80x9cdumbxe2x80x9d (i.e., not programmable).
While the intelligent devices in the network made possible a whole new array of telephone services, the intelligence was not without cost. The interactions between various kinds of services have made network behavior complex and difficult to understand and each new kind of service has meant new program code and data bases and changes to existing program code and data bases. Presently, a modern central office switch contains five million or more lines of program code. Of course, as the number of services has increased, so has the difficulty of adding new code and data bases to the system, maintaining the old code and databases, and checking the consistency of the databases and the switch""s behavior. One result of this fact is that most of the cost of a modern switch is the cost of maintaining and modifying its code; another is that it has become increasingly difficult to create and modify services with the speed required by an ever-more competitive marketplace.
The fact that intelligence was available only inside the network also affected the design of the systems that provisioned the network (i.e. modified the devices and/or configuration of the network), maintained the network, and billed the customers. As a result, the provisioning, maintenance, and billing systems are now sources of large costs in the telephone system.
While the telephone equipment providers and service providers have been struggling with the demands of programming, provisioning, and maintaining the intelligent network, advances in the technology of making integrated circuits have so reduced the cost of processors and memory that every household has formerly xe2x80x9cdumbxe2x80x9d devices such as microwave ovens or television sets which now include a considerable amount of intelligence. At the same time, advances in transmission technology and packet switching have greatly reduced the cost of actually moving information from one location to another.
It is an object of the present invention to takes advantage of the existence of low-cost programmable devices and the advances in packet switching and transmission technology to create a telephone system which is equally adapted to voice and data communication, which requires fewer switches and trunk lines than existing systems, and for which programming, maintenance, provisioning, and billing are greatly simplified, and thereby to provide telephone and other telecommunications services at a substantially lower cost than heretofore possible.
A telephone system which attains the objects of the invention is implemented in a packet network which provides virtual circuits with constrained delay and delay variation and can thereby guarantee a bound on the maximum round-trip delay time. At the edges of the network are intelligent network interface units (NIUs), which can send packets to each other via the packet network. The network interface units are connected between the packet network and standard telephone devices such as telephones or central office switches.
Control packets are used to establish virtual circuits with bounded round-trip delays between a pair of the network interface units. Once the circuits have been established, each network interface unit of the pair receives voice signals from the standard telephone device to which it is attached, makes a compressed digital representation of the voice signals, places the compressed representation in short packets addressed to the virtual circuit which takes them to the other network interface unit of the pair, and places the packets on the network. On receiving a packet, the other network interface unit decompresses the compressed representation and provides the resulting voice signal to its attached standard telephone device. Further compression is attained by means of silence detectors in the network interface units. When the silence detector detects a period of silence, the network interface unit places an indication in the compressed representation that the silence has begun and immediately sends the packet. When the silence detector detects that the period of silence has ended, the network interface unit immediately begins making a new packet.
From the point of view of the user of the standard telephone device, system 101 behaves exactly like a standard telephone network. Each network interface unit responds to control signals from the standard telephone device by making control packets and placing them on the packet network and to certain control packets received from the network by providing control signals to the standard telephone device.
Because the telephone system is implemented using a packet network and network interface units, which can produce and respond to control packets, the telephone system can be used for data as well as voice. Further, the ability of the network interface units to produce and respond to control packets means that new services can be defined in the network interface units instead of in the network. That in turn greatly simplifies the design of devices in the network. The use of packets together with voice compression and silence detection to produce the representation of the voice signals in the packets greatly reduces the amount of network resources required for a given volume of telephone calls and thereby the cost of building and running the system. The use of short packets in a packet network with bounded maximum delays permits consistent toll-quality voice reproduction.
The fact that the network interface units are intelligent operates to reduce the cost of provisioning and maintenance. The telephone system maintains a map of the network, and periodically polls the network to determine whether any new devices have been attached to it. Each new network interface unit automatically responds with the information the telephone system needs to add it to the network. The telephone system also periodically polls existing devices to determine their status, and thus always has a nearly-current map of the network.
The telephone system also employs simplified billing. Users are charged a monthly access fee and a flat per-minute rate for telephone calls, regardless of the location called. The billing data base thus need only record how many minutes a subscriber has used the network each month, and the subscriber""s telephone bill is reduced to a single line listing the access fee and the number of minutes the network was used. If the subscriber consents, the telephone system can charge the amount owed each month to the subscriber""s credit card, with the bill appearing as a line on the credit card statement.
The foregoing and other objects and advantages of the invention will be apparent to one of ordinary skill in the art who peruses the following Drawing and Detailed Description, wherein: